Design Criteria
  Structural Tree Soil
  Amended Native Soil
Plans & Details
Monitoring & Lessons Learned
  PCC Sylvania Lot 10
  Sunset Swim Center
Cost Considerations
Additional Resources
Water Quality Monitoring: PCC Sylvania
The water quality is being monitored by the City of Portland. Information will be included in their bi-annual monitoring report. A link to it will be provided when it becomes available.
Lessons Learned: PCC Sylvania

Parking Forest, one year after planting. The trees haven't been driven into or died or drought!

Challenge: We couldn't plant trees before the rains came in October since we didn't have any way of irrigating this area.

Solution: We ran 4 100-foot long hoses from the library on planting day. John Gwaltney-Beaumont said that he would treat the trees with Dri-Water, which is common practice on the campus for getting vegetation established without irrigation.

Conclusion: This seems to have worked. All three trees survived an unusually lot and hot summer.

Challenge: The original design called for wheel stops with feet that would allow water to sheet flow, more or less, into the exposed soil/gravel area. Due to lack of funds, we were grateful to have these wheel stops donated by the college; however, their continuous contact with the pavement means that runoff is concentrated and becomes erosive at the spaces inbetween them.

Solution: I hope to go place some porous pavers at the inlet to dissipate the energy and also to capture sediment and reduce weeding. Suitable products are truly porous pavers like from XeriPave.

Conclusion:I haven't tried this yet, but will let you know how it works out.

Challenge: Before the trees got planted, students were not used to having a soft spot with wheel stops in their parking lot. To my knowledge, three students jumped the wheel stop and had to have their cars pulled out of the soft soil/gravel area shown above between the beginning of September when the contractor finished his work and mid-October, which was as soon as we could plant the trees.

Solution: Maybe we should've fenced this area off until the trees were put in, but we couldn't afford to lose even 6 parking spaces during the Fall session.

Conclusion: This didn't work great, but I'm not sure how else we might've handled this and the system doesn't appear to be hurt by a few cars driving into it.

Challenge: Staff was very concerned about being able to plow effectively around the wheel stops.

Solution: It appears that the Parking Forest BMP was actually a benefit to snow plowing and a good place, like other bioretention systems, to store snow.

Conclusion: Nothing needs to be changed.

Photo Point Monitoring: Sunset Swim Center

Download the tree health assessment performed by Todd Prager, our consulting arborist, not long after the trees were planted in 2013.

Download the latest Photopoint Monitoring Report (includes Year 1 from 2013 and Year 2, completed on 10-06-2014)

Fifteen trees at the Sunset Swim Center are being photopoint monitored for a period of 10-years. There are five different species with one tree of each species in each tree trench, planted in the same relative place to the others. All the exposed tree trenches were specified to be amended natives soil: native clay soil with compost bucket mixed in (approximately 2 clay to 1 compost) and top dressed with Permamatrix (mycorrhyzae, biota, biochar, Geohumus). The trees are irrigated.

Three different conditions were created in the parking lot, using 5 different species:

  • The western most trees closest to the building (trees 1 to 5) are planted in a 4-foot wide compost-amended soil trench covered in open-graded rock, surrounded by pervious concrete and typical, very clean pervious concrete base rock. (Total trench width = 4').
  • The center line of trees (trees 6 to 10) were planted in a 4-foot wide compost-amended soil trench covered in open-graded rock, surrounded by pervious concrete over structural tree soil to an additional width of 4-feet on either side. (Total trench width = 12'). Pervious pavement on very clean pervious concrete base rock extends out from there.
  • The "control" set of trees (trees 11 to 15) were planted just outside the parking lot in a 12' wide amended native soil trench surrounded by lawn in presumably native clay soil. (Note: This amendment was never completed per plans by the landscape contractor.)


Our assumption, based on research by the USDA Forest Service and the observations of Todd Prager, our team’s arborist, is that mature canopy area is directly related to the volume of soil it can access.


Our hypotheses are as follows:

  • Trees 11-15 on the easternmost side will grow the largest and trees 1-5, the westernmost trees, will be the smallest.
  • Both sets of trees in the parking lot will grow at a similar rate until year 15 or so, when soil volume limits growth of westernmost trees.
  • The lawn trees will grow at a faster rate initially compared to parking lot trees because there is more water availability and less reflected heat/evapotranspiration than the parking lot trees.
Download the latest Photopoint Monitoring Report (Year 2, completed on 10-06-2014)
Lessons Learned at the Sunset Swim Center
Year 1 Observations

Trees were installed per plans, although the no one from our team was available to observe the soil being amended for trees 1 - 5, in the westernmost trench closest to the building. The soil amendments do not appear to have been done for trees 11 to 15.

Year 2 Observations

The native red alder trees (5 and 10) have been replaced with a different species. The native red alder tree in the control plot (15) has been removed and was not replaced.

We are currently waiting to hear from THPRD staff regarding why the native red alder trees, two of which were in "average condition" (according to the initial health assessment available for download above) and one of which was in "declining condition" were replaced. We'll let you know when we find out!
Creative Commons LicenseParking Forest Website by Green Girl LDS is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. We believe the term "Parking Forest" was coined originally by Brian Wegener of the Tualatin Riverkeepers in an email on June 29, 2013.
Green Web Hosting! This site hosted by DreamHost. This web site is hosted by DreamHost, a friendly, greeny-type company. Updated 10 Nov 2014